1. Field of the Invention
This invention relates to the mechanical bending of lead wires extending from electrical circuit packages to a desired shape for bonding onto a substrate.
2. Description of the Related Art
TAB (tape automated bonding) integrated circuit (IC) chips are generally formed with straight lead wires extending laterally out from the chip. To mount and electrically connect the chip to a circuit board or other substrate, the lead wires must be bent down so that they can make contact with bonding pads on the substrate. The ends of the lead wires that contact the bonding pads must be kept straight and parallel to the pads. For this purpose special lead wire forming tools have been used.
A typical lead wire forming operation is shown in FIG. 1. A TABed IC chip 2 has a set of lead wires 4 which initially extend laterally outward from the upper surface of the chip and are clipped to the desired length. The chip 2 is then placed on a special forming substrate 6 from which fulcrum bars 8 extend upward adjacent to the edges of the chip to support the undersides of the lead wires 4.
To conform the ends of the lead wires 4 to the substrate 6, a mechanical forming tool 10 is used. The forming tool includes a set of stamping bars 12 that extend down from the tool in alignment with the outer sections of lead wires 4. The tool 10 is lowered against the lead wires so that the stamping bars 12 force the ends of the lead wires down flat against the substrate, with the lead wires bending about the fulcrum bars 8 and again about the inner edges of the stamping bars 12. The lead wires are now properly formed so that their outer ends can be bonded to bonding pads on their mounting substrate.
While the lead wires for a particular part design can be formed in a fairly efficient manner with this type of die tool, different sets of tooling are required for each different chip and wire size. Each different set of tooling can be quite expensive, and can require a substantial lead time for delivery Also, a dedicated forming substrate with fulcrum bars 8 is necessary for each chip size.